Here is the full list of all 20 AER - there are Memories of Old achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Completed the game.
Complete the Monastery.
Find the Ancient Llamba.
Discover all areas of the map.
Speak to all of the spirit animals.
Find the dwellings of the rift cult.
Find the ancient battlefield.
Find the bones of an old beast.
Find Erin when she's gone.
Complete the Archives.
Find the statue of the fox.
Find the chiseled stone map.
Find the giant birdshrine.
Find the statue of crane.
Find the Crab Island.
Step into the well.
Complete the Eventide Sanctuary.
Get some Lambaby love.
Find the statue of the deer.
Escape the collapsing cave.